Preparation of quaternary polyvinyl pyridine polymers in water

ABSTRACT

A process in which a quaternary vinyl pyridine salt may be produced and then polymerized directly without the need for any isolation stage is disclosed. The process involves the replacement of the conventional non-aqueous solvent for the reaction by water; the vinyl pyridine and water are mixed, a quaternizing agent is added to the mixture and the mixture heated to form a solution of the quaternary vinyl pyridine salt. The solution so produced is then directly amenable to polymerization without the necessity for isolation and purification of the salt.

United States Patent Webster 51 Aug. 8, 1972 [54] PREPARATION OFQUATERNARY POLYVINYL PYRIDINE POLYMERS IN WATER [72] Inventor:

tion Road, Gnosall, Stafford, England [22] Filed: June 30, 1969 [2]]Appl. No.: 837,868

[30] Foreign Application Priority Data July 18, 1968 Great Britain..34,285/68 [52] US. Cl. ..260/294.8 R, 260/883, 260/793 M [51] Int. Cl...C07d 31/48 [58] Field of Search ..260/294.8

[56] References Cited UNITED STATES PATENTS 2,484,420 10/ 1949 Minsk etal. ..260/294.8

William E. Webster, Menai, Sta- 2,484,430 l0/l949 Sprague et al..260/294.8

Primary Examiner-Alan L. Rotman Att0rneySughrue, Rothwell, Mion, Zinn &Macpeak ABSTRACT A process in which a quaternary vinyl pyridine salt maybe produced and then polymerized directly without the need for anyisolation stage is disclosed. The process involves the replacement ofthe conventional non-aqueous solvent for the reaction by water; thevinyl pyridine and water are mixed, a quatemizing agent is added to themixture and the mixture heated to form a solution of the quaternaryvinyl pyridine salt. The solution so produced is then directly amenableto polymerization without the necessity for isolation and purificationof the salt.

6 Claims, No Drawings PREPARATION OF QUATERNARY POLYVINYL PYRIDINEPOLYWRS IN WATER There are basically two processes for the preparationof quaternary poly(vinyl pyridine) salts from vinyl pyridines; eithervinyl pyridine is polymerized and the polymer then quaternized, or avinyl pyridine itself is quaternized and the quaternary salt thenpolymerized. Of these two processes, the latter is the more recent, andhas certain advantages. One way of carrying out the latter process isdescribed in US. Pat. No 2,811,510 in which 2-methyl-5-vinyl pyridineand a dialkyl sulphate are reacted together in acetone at lowtemperature whereupon the quaternary vinyl pyridine salt is precipitatedas a white crystalline solid. This salt as precipitated containsimpurities, and is recrystallized from ethanol, and then dissolved inwater and polymerized at 60C, using a peroxide initiator in suchconcentrations as to promote free radical polymerization. The viscoussolution resulting is diluted with an equal volume of methanol, andpoured into acetone when the quaternary poly (vinyl pyridine) salt isprecipitated.

One problem with the above described process is the need to isolate thecrystalline quaternary salt prior to polymerization. Further thecrystallization process can only be applied to vinyl pyridines having amethyl group adjacent to the heterocyclic nitrogen atom. The

,corresponding crystalline salts of vinyl pyridine monomers such as2-vinyl pyridine, 4-vinyl pyridine and 5-ethyl-2-vinyl pyridine cannotbe formed in the manner described.

There has thus been a need for a process in which a quaternary vinylpyridine salt may be produced and then polymerized directly without theneed for any isolation stage. It is clearly desirable that any processdeveloped should be applicable to vinyl pyridines ir respective ofwhether a methyl group is present in the position adjacent to theheterocyclic nitrogen atom.

This has been achieved by replacing the conventional non-aqueous solventfor the reaction by water. Thus, according to the invention, I mix avinyl pyridine and water, add a quaternizing agent to the mixture andheat to form a solution of the quaternary vinyl pyridine salt. Thesolution so produced is then directly amenable to polymerization withoutthe necessity for isolation and purification of the salt.

Various quaternizing agents may be used, but the preferred agent is adialkyl sulphate, the simplest example of which is dimethyl sulphate,and the invention will be further described primarily with reference todimethyl sulphate although other agents such as diethyl sulphate can beused equally well. It is surprising that the process according to theinvention can be carried out using dialkyl sulphates such as dimethylsulphate. Dimethyl sulphate, for example, is stated in the literature tobe hydrolyzed by water at or above 18C, and therefore one would haveexpected that heating an aqueous mixture of a vinyl pyridine anddimethyl sulphate would result in a considerable quantity of thedimethyl sulphate undergoing hydrolysis; this is not so as may be seenfrom the yields of 95 percent or better of quaternary vinyl pyridinesalt which can be obtained by heating to 70C. The quantity ofquaternizing agent required is nominally one molar proportion, referredto the vinyl pyridine. In practice however, purity factors of thereactants have to be taken into account and the precise quantityrequired is detemiined by analysis of a sample withdrawn from thereaction mixture at an appropriate time.

The polymerization of quaternary vinyl pyridine salts in aqueoussolution has in recent years been studied in some detail, and it hasbeen found that polymerization may occur by one of two mechanisms, afree-radical mechanism as described by Shyluk, Poly(1,2-dimethyl-S-vinyl pyridinium methyl sulphate) l, polymerization studies,Journal of Polymer Science, Pt. A 2(5) 2191-2206 (1964), or aspontaneous polymerization mechanism, as described in Spontaneouspolymerization of 1,2 dimethyl 5-vinyl pyridinium methyl sulphate in anaqueous medium. Dokl Acad. Nauk; USSR, 168 (0) 1350-3 1966. There areessential differences between the two mechanisms of polymerization,however, as regards the necessary concentration of the quaternarypyridine salt, the level of initiation, and the temperature ofpolymerization. In free radical polymerization, complete conversion ofquaternary pyridine salt to polymer can be made to occur at almost anytemperature and at almost any concentration of the salt, the rate ofpolymerization increasing with increase of temperature, and the level ofinitiation necessary being inversely related to the salt concentration.At low concentrations, for example 10-25 percent of salt, as much as 5percent of initiator may be necessary while at higher concentrations,such as 50-90 percent of salt, the amount of initiator required may bereduced by a factor between 10 and a hundred. For spontaneouspolymerization to occur, the concentration of the salt must be veryclose to its maximum solubility, and high conversions of salt to polymerare only obtained if the temperature is kept at or below about 30C;above this temperature; at best 60 percent conversions can be obtained.Considerably less initiator is required than in free radicalpolymerization, and up to 1,000 ppm. of initiator, or mere exposure toair, will generally suffice.

Solutions of quaternary vinyl pyridine salts prepared according to theinvention are very suitable for spontaneous polymerization, since theycan be prepared in very concentrated form. There is no need to purifythe quaternary salt before polymerization; such hydrolysis products ofthe dialkyl sulphate as are produced, and free sulphur dioxide, (whichmay frequently be present in commercial dialkyl sulphate), do notinhibit the subsequent polymerization. The quantity of water in theinitial reaction is determined by the concentration of monomerquaternary salt required. This concentration is governed by two factors:

a. The minimum monomer quaternary concentration for the polymerizationto occur in the manner required, and

. desirability of the formation of the polymer in a hard, brittle andtherefore easily handleable form, or in the case of rubbery polymers eg.using 2- methyl 5-vinyl pyridine, as a tough elastic material. Forexample, if 1 mole 2-vinyl S-ethyl pyridine and 1.05 mole water areheated to C and quaternized by adding 1 mole dimethyl sulphate, theresulting monomer quaternary salt solution contains percent monomersalts and 5 percent water. At this concentration, polymerization occurson adding 100 ppm ammonium persulphate and a hard brittle polymer isformed.

One important aspect of our invention, however, is that we have foundthat there is a critical concentration of free vinyl pyridine in thequaternary salt solution(expressed hereafter as a percentage of thevinyl pyridine taken initially and not as a percentage of the totalsolution)above which spontaneous polymerization will not occur to anyappreciable extent. For example, in the case of 2-vinyl pyridine,polymerization is seriously retarded if there is more than 0.5 percentof free 2-vinyl pyridine present in the quaternary salt solution. If allthe other conditions are suitable for polymerization, that is the saythe temperature and the concentrations of salt and initiator, and yetpolymerization does not take place satisfactorily, then it may beassumed that there is too much free vinyl pyridine present. A sample ofthe solution must therefore be tested at this stage, for

example by standard ultra-violet spectrographic techniques or bytitration, and if the content of free vinyl pyridine is above that whichexperience has shown to be the critical level, then small furtheramounts of quatemizing agent must be added. A typical solution containsthe quaternary salt, together with free vinyl pyridine and vinylpyridine present as simple salt formed by the reaction of vinyl pyridineand acids produced by any small amount of hydrolysis of dialkyl sulphatethat has occurred. One method of testing is as follows: A sample of thesolution is diluted with water and extracted with benzene. The benzenelayer which contains any free vinyl pyridine is titratedagainst 0.1Nacetous perchloride acid to the grey-green end point using crystalviolet indicator. The raffinate is then basifred to liberate the vinylpyridine present as simple salt and extracted again with benzene andtitrated as before. From the quantity of vinyl pyridine taken at thestart of the preparation, the concentration of free vinyl pyridine andof vinyl pyridine as simple salt, the concentration of quatemized saltcan be calculated. Additional dialkyl sulphate is added according to thefree vinyl pyridine found by the first titration.

The solution is then cooled and a small proportion of initiator added sothat spontaneous polymerization occurs; the temperature at whichpolymerization takes place should preferably be between 20 and C, andany increase in temperature will result in a fall in the conversion.Quaternary poly(vinyl pyridine) salt is ob tained as a brittle solid orstiff rubber depending on the particular vinyl pyridine being used.

The invention is applicable primarily to the formation of quaternarysalts (and thereafter of polymers) from a vinyl pyridine itself or frommonoor dialkyl vinyl pyridines, such as ethyl or methyl vinyl pyridines.The vinyl group may be in the 2, 3 or 4-position on the pyridine ring,but the process does not give such outstandingly good results when thevinyl group is in the 4- position. Specific examples of the vinylpyridines which may be used are 2-, 3-, or 4-vinyl pyridine,

2-vinyl, S-ethyl pyridine,

2-methyl 5-vinyl pyridine, 2-vinyl 4-methyl pyridine,

Z-methyl 6-vinyl pyridine, 2-methyl 4-vinyl pyridine,

2-vinyl S-methyl pyridine,

3-vinyl S-ethyl pyridine,

2-vinyl 4,6 dimethyl pyridine,

4-vinyl 2,6 dimethyl pyridine,

2-isopropenyl pyridine, and

4-isopropenyl pyridine, the process being particularly effective for2-vinyl pyridine,

2-methyl 5-vinyl pyridine and 2-vinyl 5-ethyl pyridine The preferredtemperature for the quatemization is from 50 to 90C although thereaction can be carried out less successfully outside this range. Theoptimum temperature for the quatemization is about C and a typicalconversion at this temperature is 95 percent.

As stated, for spontaneous polymerization, the concentration of thequaternary vinyl pyridine salt in solution must be close to its maximumsolubility. ln practice this means that the concentration must be, forexample, at least percent in the case of 2-methyl-5- vinylpyridine-dimethyl sulphate salt, at least percent in the case of 2-vinylpyridine-dimethyl sulphate salt and at least percent in the case of2-vinyl 5-ethyl' pyridine-dimethyl sulphate-salt. As stated previously,spontaneous polymerization may be induced by mere exposure of thequaternary salt solution to air but in practice this is not asatisfactory procedure since precise control of the level of initiationproduced is not possible. In practice very small concentrations ofinitiator are added, the amount being determined by the particular vinylpyridine involved. Ammonium or other persulphates are the preferredinitiators, and then we prefer to use about 25 p.p.m. for 2-vinylpyridine, from to p.p.m. for 2-methyl-5-vinyl pyridine, and from 25 to75 p.p.m. for 5-ethyl 2-vinyl pyridine.

Concentrations of initiator in excess of these levels can result indangerous runaway polymerizations where the temperature increase cannotbe controlled, unless the plant is so designed that it has a suitablereserve of cooling capacity to meet such eventualities.

Other suitable initiators include organic peroxides and AZDN, (N,Nazodiisobutyronitrile).

Some examples will now be given:

EXAMPLE 1 1 mole (126 g) of dimethyl sulphate was slowly added to anaqueous solution of 1 mole (119g) of 2- methyl-S-vinyl pyridine and 82gof water. The reaction was exothermic, and the temperature wascontrolled at 60C by the rate of addition of the dimethyl sulphate; thereaction was completed in 30 minutes.

The solution was cooled to 20C, and 150 p.p.m. of ammonium persulphateadded. Polymerization proceeded rapidly, and a tough rubbery gel of poly1,2-dimethyl-5-vinyl pyridinium methosulphate) in 93 percent yield wasobtained in 3 hours.

EXAMPLE 2 1 mole (126 g) of dimethyl sulphate was slowly added to anaqueous solution of 1 mole (133 g) of 5- ethyl-2-vinyl pyridine and 5gof water. The procedure of example 1 was followed, and a 97 percentyield of poly l-methyl-S-ethyl-Z-vinyl pyridium methosulphate) obtainedas a brittle polymer.

EXAMPLE 3 1 mole of 5-ethyl-2-vinyl pyridine and 1.05 mole of water weremixed and heated to 70C. 1 mole diethyl sulphate was added stepwise,maintaining the temperature between 65C and 75C. The resulting solutioncontained nominally 95 percent monomer salt and after cooling to 25C andadding 100 ppm ammonium persulphate, a hard brittle polymer was formedduring 3-4 hours.

EXAMPLE 4 Into a 7 gallon reactor fitted with a 5 inch turbine agitatorand baffle was charged 15.75 lb of 2-vinyl pyridine and 1.85 lb water.The temperature was raised to 65C and 19.3 lb of dimethyl sulphate wereadded in small aliquots, the temperature being maintained at 70 2 5C bysupplying cooling water as required to a jacket surrounding the reactor.The quaternization stage was completed in 50 minutes.

The batch was analyzed for free 2-vinyl pyridine at this point andsufficient dimethyl sulphate added to reduce the level of free 2-vinylpyridine to below 0.4 percent. The mixture was then cooled with stirringto room temperature, 15.8 ml of 5 percent w/w aqueous ammoniumpersulphate solution were added and the mixture stirred for 2 minutes.The initiated batch was then placed in polyethylene-lined, water cooled,metal trays for polymerization, the temperature during thepolymerization process being maintained at 25 i 5C.

The conversion to polymer was 80 percent within 3 hours and poly(l-methyl-Z-vinyl pyridinium methosulphate) was obtained as a brittlesolid. Quaternary poly(vinyl pyridine) salts are useful as flocculantsfor anionic suspensions including clays, shales, coal fines, sewagesludges and colloids such as humic acids. One important application isin their use as conditioning agents to aid the de-watering of sewagesludges and similar concentrates, and further applications include theiruse as antistatic agents, mordants for acid dyes, adhesion aids, surfaceconditioning agents, and in the formation of complexes with acidicpolymers. The solid or rubbery polymers are generally used in aqueoussolution. For example, a 1 percent solution may be added to sewagesludge and the resulting flocculated solids are easily dewatered. Thepolymers are used similarly in flocculating suspended fines in coal washwaters, clay slurn'es and so on.

When used for example as an adhesion aid or size, again the polymer isapplied to a substrate by adsorption from an aqueous solution.

Iclaim:

1. A process for the preparation of a quaternary vinyl pyridine salt inwhich a vinyl pyridine is mixed with water, a quaternizing agent isadded to the mixture and the mixture heated to form a solution of thequaternary vinyl pyridine salt.

2. A process according to claim 1 in which the quaternizing agent is adialkyl sulphate.

3. A process according to claim 2 in which the quaternizing agent isdimethyl sulphate.

4. A process according to claim 2 in which the quaternizationtemperature is from about 50 to about 90C.

5. A process according to claim 4 in which the quaternizationtemperature is about C.

6. A process according to claim 4 in which the vinyl pyridine is2-methyl-5avinyl pyridine, 2-vinyl pyridine or 5-ethyl-2-vinyl pyridine.

UNITED STATES PATENT eTTTtE QERTIFICATE @f @QRREUHQN Patent No. 3, 82,939 Dated August 8, 1972 Inventor(s) William E Webster It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In The Heading:

The name of the Assignee was omitted. Should read:

--Assignee: Midland-Yorkshire Tar Distillers Ltd.

Birmingham, England- Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PO-105O (10-69) USCOMM-DC 60376-P69 n u.s. GOVERNMENTPRINYING OFFICE: 1959 o-ass-ssa

2. A process according to claim 1 in which the quaternizing agent is adialkyl sulphate.
 3. A process according to claim 2 in which thequaternizing agent is dimethyl sulphate.
 4. A process according to claim2 in which the quaternization temperature is from about 50* to about90*C.
 5. A process according to claim 4 in which the quaternizationtemperature is about 70*C.
 6. A process according to claim 4 in whichthe vinyl pyridine is 2-methyl-5-vinyl pyridine, 2-vinyl pyridine or5-ethyl-2-vinyl pyridine.